The present invention relates primarily to a method of producing a plastic product having at least one outer surface assigned a microstructure, utilising an arrangement for moulding plastic products.
This arrangement for producing plastic products has at least two mould parts movable towards and away from each other, a predetermined volume or quantity of a viscous polymerisable plastic material being supplied to a first cavity formed between the mould parts.
By the expression xe2x80x9cpolymerisable plastic materialsxe2x80x9d is meant a plastic material having a viscosity equivalent to that of water or thinly fluid syrup.
The method in accordance with the invention is designed for use in both die-casting and compression moulding.
In the case of die-casting the mould parts assume a co-operating position in relation to each other and a cavity formed between the mould parts has a shape conforming to an outer shape of the plastic product, viscous plastic material being pressed into the cavity and being permitted to polymerise there.
In the case of compression moulding the mould parts shall be able to assume an almost fully united position in order to allow a predetermined volume or quantity of a viscous polymerisable plastic material to be supplied to a first cavity formed between the mould parts.
The method in accordance with the invention is thus based on the mould parts being subsequently compressed to a fully united position and said viscous plastic material being distributed under a positive pressure within a smaller second cavity corresponding to the shape of the final plastic product, the outer form of which will conform to the internal shape of the second cavity formed by the mould parts.
The defining inner surfaces of the second cavity will thus correspond to the outer defining surfaces for the final product. However, each microstructured surface portion of the final product will have its corresponding microstructured surface portion in the second cavity.
Polymerisation of the viscous plastic material is then performed, with the mould parts in fully united position and, after said polymerisation of the plastic material, the mould parts are caused to move apart from each other to allow removal of a finished plastic product from the second cavity formed by the mould parts.
In this context it should be mentioned that by the expression xe2x80x9cpolymerisable plastic materialxe2x80x9d is meant a plastic which is supplied in thinly fluid form to a first cavity formed between the mould parts and which is distributed in its thinly fluid form within a second cavity by the movement of the mould parts towards each other, thereby filling out and penetrating into the surface portions of the microstructure in one or more mould parts, whereafter measures are taken to cure or polymerise the plastic material in the second cavity.
Polymerisation of the plastic material may be carried out by means of various known methods.
For instance an addition curing component may be added to the plastic material used, a so-called two-component system, or a plastic material may be chosen that is cured when subjected to light such as UV (ultraviolet) light, a plastic material curable when subjected to heat, or a plastic material with catalytic properties for polymerising, etc.
Thus the invention is not based primarily on the use of such viscous thermoplastic materials with which a desired curing shall occur by a hot plastic material being introduced under a positive pressure between fully united mould parts forming said second cavity and where the curing occurs by cooling of the mould parts and the inner structure of the second cavity.
The invention relates secondly to an arrangement for producing plastic products, designed to enable performance of the method in accordance with the invention.
Although the invention may be applied in the die-casting technology the significant properties of the invention will be illustrated in the following in the compression moulding technology, utilising a viscous polymerisable plastic material.
Various methods have been proposed for producing a plastic product with microstructured surface portions, utilising an arrangement for producing plastic products.
Considering the application so significant for the present invention, namely the prime object of providing a method and an arrangement for producing plastic products for the manufacture of plastic discs containing information, such as CD discs, DVD discs or, in a wider application, micromechanical discs of various types, a plurality of methods and arrangements are known.
Microfluids fall within the latter application, where a fluid shall pass through channels in the disc formed by means of micromechanics, for measuring various entities. Open channels in the surface may here be covered by a lid in order to form closed channels in the surface.
A more specific application is to allow winding channels to be formed on a disc in order to separate different DNA molecules with electrophoresis. A voltage forces the molecules forward and an optical detector registers when they arrive.
The microstructure of CD discs and storage of information currently has a height of 0.1 xcexcm and a breadth (elevation and depression) of 0.7 xcexcm.
The microstructure useful in microfluids for flow handling and optics may have a height of 10-100 xcexcm and a channel breadth of 20-100 xcexcm.
For information storage it is known to produce CD discs with high or extremely high storage capacity.
In this context it should be mentioned that CD discs of the type under discussion have been given various designations for the relevant storage capacity, such as DVD5, DVD8 (Digital Versatile Disc), where the figure stated indicates the storage capacity in Gbyte.
An arrangement for producing plastic products which is currently extremely useful for producing such CD discs is the use of an injection moulding machine for thermoplastics where two mould parts used shall assume a position fully co-operating with each other and where the mould parts form said second cavity.
In this co-operating position a heated thermoplastic compound, in the form of a plastic composite, is pressed through a fixed mould part to a space or a second cavity formed between the two mould parts, for die-casting of a flat plastic component with microstructured surface portions.
The movable mould part is then moved away from the fixed mould part and the formed flat moulded plastic component or the CD disc is removed from the movable mould part.
In this application curing of the thermoplastic material occurs through a considerable drop in temperature, usually in the order of 100xc2x0 C. The drop in temperature stated here applies to the difference between the temperature of the feeding screw and of the plastic product upon removal from the mould parts.
The ambition to maintain a high rate of manufacture demands a temperature in the mould parts and the second cavity that has a cooling and curing effect on the thermoplastic material supplied, with reduction of the replication ability as regards the microstructured surface section.
However, the present invention is also based on an, albeit, previously known method of producing a plastic product and an arrangement for producing plastic products which, as a result of the thermoplastic-based manufacturing method described has been pushed aside since, with current technology and demands, it has been considered too expensive and too slow. This method with an arrangement for producing plastic products has therefore only be used to a limited extent for producing genuine, complete plastic products with one or more microstructured surfaces.
The method and the arrangement for producing plastic products from which the present invention can be deemed to emanate are shown and described in more detail in the publication xe2x80x9cHigh Density CD and Industrial approachxe2x80x9d, publication number ISBM 90-80 2001-2-3, particularly pages 77-79.
The method and arrangement for producing plastic products from which the present invention has been developed are described in more detail with reference to the following FIGS. 1 and 2.
The advantage with this method and the associated arrangement for producing plastic products is that the replication capacity is good, thanks to a polymerisation of the plastic material, in that a viscous plastic material can be pressed out into a second space and is only thereafter activated so that polymerisation occurs.
Additional examples of the state of the prior art are shown and described in the following patent publications:
EP-A1-0 628 957
Here is shown and described an arrangement for injection moulding of optical recording blanks comprising two mould parts, moveable towards each other, which are designed and displaceable in order to form a cavity between them, corresponding to the shape of the recording blank.
Referring now to FIG. 6, the arrangement is shown in cross-section and from this figure it can be seen that a polycarbonate-based plastic shall be pressed in a moulding apparatus based on the principle of injection.
The moulding process, for the manufacturing of an optical disc substrate, is based upon that an outer edge (21a) for the movable mould part (21) shall be brought into contact with the upper surface (28a) for the mould support (28) and which is arranged at the periphery of the lateral side part (22) of the cavity in order to close the mould.
In this position, the plastic material is injected from the orifice (27) and the nozzle (13) and into the space (20). During this injection process, the space is opened by the moveable part (21) being displaced from this space according to FIG. 7, and subsequently the parts are pressed together again towards the position shown in FIG. 6, according to FIG. 8.
It should especially be noted that the finished product will here comprise of an entire disc, (the central part of which does not display a hole) the central portion of which however is formed with a thinner area (of the part 24) and to this area is integrally attached a funnel-shaped part, cured by cooling and having the shape of a truncated cone, which must be regarded as a residual product.
The thinner portion and the funnel-shaped part shall be separated through punching, in an operation completely separated from the moulding process, in order to subsequently be able to have a disc-form with a centrally oriented hole.
To continue, it is obvious that the technique shown and described here, is based on die-casting or compression moulding of a plastic material, which is made slightly viscous through heating, and through a reduction of temperature in the mould is allowed to solidify to a disc substrate.
EP-A1-0 540 843
Here is shown and described a process for producing optical discs. It is proposed that onto a substrate (3), made of silicone, quartz, glass or metal, is applied a photo-resistant in the shape of a layer (1) and through exposure to light, developing and etching, a punch or stamper (6) is obtained and thereby a duplication may be achieved of an information pattern for an optical disc substrate by using a plastic, curable by means of UV light, a polymerised plastic material which is also used in the present invention.
Technical Problems
Considering the circumstance that the technical deliberations one skilled in the relevant art must perform in order to be able to offer a solution to one or more technical problems posed are initially an insight into the measures and/or the sequence of measures that must be taken and a choice of the means required, and on the basis thereof, the subsequent technical problems should be relevant in arriving at the present invention.
Considering the earlier state of the art as described above, and utilising a method described more fully in the preamble to claim 1, and also an arrangement for producing plastic products described more fully in the preamble to claim 15, it should be deemed a technical problem to make use of the principles for the, methods and the arrangement for producing plastic products described more fully in the above-mentioned publications, in order rationally, at lower cost and observing higher precision, to be able to create such conditions that a plastic product can be produced having microstructure-related surface portions of various types.
A technical problem exists, using simple measures, in being able to create such conditions that a viscous polymerisable plastic material can be supplied in a ring-shape to a cavity, such as around a hole pertaining to the finished plastic product, and that said viscous plastic material is distributed in a radial direction from said hole towards the peripheral edge area or areas of the plastic product.
A technical problem also exists, using simple measures, in being able to create conditions for producing a plastic product with surface portions assigned a microstructure where the microstructure can be chosen fine for storing information and/or coarse for other technical applications, such as microfluids.
It should furthermore be considered a technical problem, using simple measures, to be able to create such conditions that the plastic product can be produced by die-casting or compression moulding.
A technical problem is also entailed in an application of this type, in being able to realise the significance of and advantages associated with being able to attach a substrate to one mould part, to which substrate the thin polymerisable plastic material shall adhere during the polymerisation.
A technical problem is also entailed in being able to realise the significance of and advantages associated with one of the substrate""s or the insert""s surfaces defining the cavity having a microstructure or alternatively being covered by a layer.
A technical problem is also entailed in being able to realise the significance of and advantages associated with one cavity-defining surface or an insert related thereto of a second mould part having a microstructure.
A technical problem is also entailed in being able to realise the significance of allowing said second cavity to have the shape and thickness of a CD disc, or thinner, or the like, said second cavity being defined by the insert by an outer concentric circular ring around the peripheral edge area.
A technical problem is also entailed in being able to realise the significance of and advantages associated with said substrate or insert forming an outer, annular ridge, the latter provided with narrow grooves.
A technical problem is also entailed in being able to realise the significance of and advantages associated with letting said outer ring delimit the distribution of the plastic material before polymerisation by means of measures entailing curing by means of light or the like.
A technical problem is also entailed in being able to realise the significance of said viscous plastic material being supplied to said cavity under positive pressure and by a circular valve arrangement.
A technical problem is also entailed in being able to realise the significance of and advantages associated with said first and second cavities being placed under negative pressure until the mould parts have been moved to said fully united position.
It would appear to be a technical problem, using simple measures, to be able to create such conditions that said cavity is placed under negative pressure, at least while the viscous plastic material is being injected.
Solution
In order to solve one or more of the technical problems listed above, the present invention commences from a method of producing a plastic product having at least one microstructured surface or surface portion, utilising an arrangement for producing plastic products.
This arrangement shall be provided with at least two mould parts movable towards and away from each other, a predetermined volume of a viscous polymerisable plastic material being supplied to a cavity formed between the mould parts and that, after said polymerisation of the plastic material, the mould parts are caused to move apart from each other to allow removal of a finished plastic product the outer shape of which conforms to the inner shape of a cavity produced by the mould parts.
The invention specifies that said viscous polymerisable plastic material shall be supplied to a cavity around a hole pertaining to the finished plastic product, and that said viscous plastic material shall, through the displacement movement of the mould parts towards each other or similar, be distributed in a direction from said hole towards the peripheral edge area of the plastic product.
Suggested embodiments falling within the scope of the present invention include that, if the plastic product is produced by means of die-casting, when said mould parts assume a fully united position the viscous polymerisable plastic material is pressed in within a central area of the finished plastic product and in proximity to a hole allocated to the plastic product.
If the plastic product is produced by means of compression moulding, in an almost fully united position of the mould parts and a first cavity thus formed between the mould parts, a predetermined volume of a viscous polymerisable plastic material is supplied to said first cavity, after which the mould parts are pressed together to a fully united position in order to distribute said plastic material within a second cavity the inner shape of which corresponds to the outer shape of the final plastic product, whereafter polymerisation of the plastic material occurs with the mould parts in a fully united position, then said viscous polymerisable plastic material shall be supplied to the first cavity within the central area of the finished plastic product and in proximity to a hole allocated to the plastic product.
Furthermore, it is proposed that, upon movement of the mould parts towards a fully united position, said viscous plastic material shall be distributed within the cavity in a direction from said hole and towards the peripheral edge area of the plastic product.
When producing a symmetrical disc the plastic material shall be supplied around a centrally located hole and the plastic material shall spread in radial direction.
Suggested embodiments failing within the scope of the present invention also include that an insert or a substrate may be attached to at least one of the mould parts, to which insert or substrate the polymerisable plastic material shall adheres after polymerisation.
Also proposed is that one of the substrate""s surfaces defining the cavity may have a microstructure, preferably covered by a semi-reflecting layer.
Also proposed is for one cavity-defining surface (or insert) of a second mould part to be partially or entirely microstructured.
The invention also proposes that said second cavity be defined by an outer circular ring formed in an insert or in a substrate around a peripheral edge area before measures are taken to polymerise a plastic material enclosed in the second cavity.
Also proposed is for said substrate to be provided with an outer, annular ridge, the latter provided with narrow groves.
Said outer circular ring may also be formed by means of surface determined measures for curing by means of light or the like.
Said viscous plastic material shall be supplied to said first cavity under positive pressure and via a circular valve arrangement.
Said first cavity shall preferably be placed under negative pressure until and when the mould parts have been moved to said fully united position.
Advantages
The advantages that can be primarily considered significant for a method and an arrangement for producing plastic products in accordance with the invention are that conditions are thus created allowing a plastic material to be used which is not cured by adjusted temperature drops, to produce either discs with a fine microstructure and high storage capacity or discs with a coarse microstructure suitable for other applications in the microstructure field, such as microfluids.
The invention enables the use of a viscous plastic material with low temperature which gives good replication capability and where curing or polymerisation occurs through measures other than drops in temperature, such as by being subjected to the influence of light, e.g. UV light.
The present invention also enables the manufacture of discs for storing information, having high storage capacity, by offering at least two reflecting layers of microstructures where a first information surface must be semi-reflecting with a reflection factor of between 20 and 40%.
The principal features of a method in accordance with the present invention are defined in the characterizing part of the appended claim 1 and the principal features of an arrangement for producing plastic products in accordance with the invention are defined in the characterizing part of the appended claim 15.